CP: Pause UIScene migration (#170490) (#170569)

CP of #170490

This PR rolls back auto-migrating iOS apps to UIScene lifecycle. It also updates tests to ensure things work in both a state where UIScene lifecycle is already adopted and when it isn't.

A number of UIScene issues have emerged since landing this in master: #170171

In addition, there's is disagreement over how some of it is implemented.

Impacted Users: All Flutter iOS developers
Impact Description: Some method channels may crash and apps using app lifecycle events may not work properly.
Workaround: Manually removing UIApplicationSceneManifest from Info.plist and potentially also update AppDelegate.swift.
Risk: Low
Test Coverage: Yes
Validation Steps: Run `flutter build ios` and see that `UIApplicationSceneManifest` if not added to Info.plist.

Update `engine.version` (#170560)

Workaround for #170536.

Prepare to publish 3.32.3, update changelog+engine.version. (#170470)

Re-update `engine.version` for 3.32.2 stable hotfix release to the la…

…st SHA with engine change (#170005)

Corrects `engine.version` for 3.32.2 stable hotfix release to the last cherry-pick SHA with an engine change: 
1091508

Point to previous commit for engine version for 3.33-0.2 (#169682)

The other commit didn't actually change any engine files, so the thing that validates when releasing failed. Rolling to point at the previous commit instead.

Update engine.version and changelog for upcoming stable release 3.32.1 (

#169619)

Update engine.version and changelog for upcoming stable release 3.32.1

[3.33] Update `engine.version`. (#169146)

Updates `engine.version` to prepare `3.33.0-0.1.pre`.

Towards #169081.

[3.32] Set engine.version to `18818009497c581ede5d8a3b8b833b81d00cebb…

…7`. (#169082)

Sets to 1881800, the last git SHA.

[3.32] Update `bin/internal/engine.version` to latest SHA. (#168979)

Update `engine.version` (#168601)

Rolls up to last commit on this branch: 38e19d0.